“Nanocomposites and nanomaterials”
Semiconductor layered structure with nanosized Nafion
membranes for new selective gas sensor
T.I. Gorbanyuk1, V.G. Lytovchenko1, I.I. Drozhcha1, S.A. Nicolskii2
1 V.E. Lashkaryov Institute of Semiconductor Physics, Natl. Acad. of Sci. of
Ukraine. Prospect Nauki, 41, Kiev-03028, Ukraine.
E-mail: [email protected]
2 Institute of High Technologies, Taras Shevchenko National University of Kyiv,
Academician Glushkov avenue 4G, 03022 Kyiv, Ukraine.
Developments of the express sensors for different types of gases (especially
environment dangerous gases) remain the important subject of research during
many recent decades. The main tasks are a improving the sensitivity, selectivity
and speed performance of signal. Clarification of the sensitivity mechanisms of the
action of adsorbed molecules, which are based on the so-called adsorbo-electric
effect, i.e. charging of semiconductor surface during adsorption actively
investigated. One of the ways control adsorption sensitivity is coadsorption –
procedure when additional adsorption changes the dielectric constant εs. Thus it
contributes to the principal weakening of the polar bonds of adsorbed molecules εa,
(remaining relatively neutral due to strong chemical bonds). In partial, such
environment is adsorbed layers of water molecules. To avoid the influence of these
dipole molecules can be used a proton conducting membrane from Nafion
perforated polymer. Nafion allows accumulating H2O molecule, creating an
environment with high ε, but does not penetration for water molecules to the
semiconductor interface. Instead, it promotes of dissociation of studied molecules
with a weak chemical bond. The next chemical reactions are probable with
hydrogen generation (H and/or H2): H2S → 2H + S; NH3 → NH + H2. So coadsorption the molecules H2S, NH3, H2O vapor etc. will produce the “useful”
electro-absorption effect of H2S, NH3, while adsorption H2O molecules does not
give effect as H2O molecules are blocked by nanomembrane.
In the present it produced structures based on porous silicon (por-Si) and
polymer films nafion/TiO2 with content TiO2 ~1%, 3% and 5% and samples
nafion/TiO2/por-Si with catalytically active Pd film on the surface. The sensitivity
of these structures were studied to vapor H2O (RH = 50%) and H2S/N2 with a
concentration of 70 ppm at room temperature. It was found that the layered
composite structure based on nafion/TiO2/por-Si films with catalytically active Pd
on the surface exhibit increased sensitivity to adsorbed H 2S molecules in the
atmosphere with water vapor.